Neuropeptides are very important messengers of nervous communication in animals. Among these neuropeptides, the tachykinin family, which contains multifunctional polypeptides exhibiting a structural homology in respect of their COOH-terminal portion, are known in particular. These polypeptides possess in common the following amino acid sequence at their COOH-terminal end: EQU Phe-Xaa-Gly-Leu-Met-NH.sub.2
in which X is a variable aromatic or branched aliphatic amino acid.
Several polypeptides of the tachykinin family have been isolated and characterized to date, from frog skin (ERSPAMER et al. 1981, Trends Neurosci. 4, 267-269). Other studies have enabled several polypeptides of the tachykinin family to be isolated from different vertebrate species.
The tachykinins in amphibians may be grouped in sub-families established in accordance with the nature of the variable amino acid residue Xaa in the COOH-terminal region. Thus, the physalaemin sub-family in which Xaa in the formula given above is a tyrosine residue (Tyr), the eledoisin sub-family in which Xaa is an isoleucine residue (IIe) and the kassinin sub-family in which Xaa is a valine residue (Val) are known.
One particular tachykinin known independently of its presence in frogs is substance P described by CHANG and LEEMAN (J. Biol. Chem. 245, 4784-4790, 1970). Studies carried out to data in Rana esculenta frogs, and in particular on the brain of this frog, have demonstrated the presence of a nerve network in the brain of this frog by means of immuno-histochemical examinations employing antisera to substrate P (GAUDINO et al. 1980, Cell Tissue Res. 211, 241-250).
Another molecule of the tachykinin family is neurokinin B described by KANGAWA et al. (Biochem. Biophys. Res. Commun. 114, 533-540, 1983).
Despite the results obtained with antibodies directed towards substance P in frog's brain, the inventors of the present application have shown that substance P does not exist in frog's brain. On the other hand, the inventors have demonstrated and characterized a new peptide of the tachykinin family belonging to the physalaemin sub-family from the brain of the Rana ridibunda frog.
From this new peptide, referred to as ranakinin, they have defined a new group of peptides having in common an amino acid structure determined from the structure of ranakinin.
The invention also relates to the preparation of the peptides defined in the following pages, as well as to their use, for example, in pharmacological applications.
The peptides according to the invention are characterized in that they correspond to the following sequence of amino acids: EQU Xaa.sub.1 Pro Xaa.sub.2 Pro Xaa.sub.3 Xaa.sub.4 Phe Tyr Gly Leu Met
in which Xaa.sub.n with n equal to 1,2,3 or 4, represents any amino acid.
The list of variable amino acids, Xaa.sub.n, capable of participating in the composition of this peptide is presented below with the abbreviation corresponding to each amino acid in the form of the three-letter code.
______________________________________ Amino acid Three-letter code ______________________________________ Alanine Ala Arginine Arg Asparagine Asn Aspartic acid Asp Asparagine or aspartic acid Asx Cysteine Cys Glutamine Gln Glutamic acid Glu Glutamine or glutamic acid Glx Glycine Gly Histidine His Isoleucine Ile Leucine Leu Lysine Lys Methionine Met Phenylalanine Phe Proline Pro Serine Ser Threonine Thr Tryptophan Trp Tyrosine Tyr Valine Val ______________________________________
According to a first particular embodiment of the invention, Xaa.sub.1 is a basic type amino acid, for example arginine, glutamic acid and preferably lysine.
According to another particular embodiment of the invention, Xaa.sub.2 is lysine, aspartic acid or preferably asparagine.
In another particular embodiment of the invention, Xaa.sub.3 is glutamine, lysine or preferably arginine.
Advantageously, Xaa.sub.4 may be selected from the following amino acids: glutamine, lysine or preferably arginine.
It is understood that the different subgroups of peptides defined by the choice of particular amino acids for Xaa.sub.1, Xaa.sub.2, Xaa.sub.3 and Xaa.sub.4 may be combined with one another, and consequently all such combinations between the different amino acids mentioned for Xaa.sub.1, Xaa.sub.2, Xaa.sub.3 and Xaa.sub.4 in the context of the amino acids sequence given above do form part of the invention.
An especially preferred peptide in the context of the implementation of the invention is that which corresponds to the following sequence of amino acids: EQU Lys Pro Asn Pro Glu Arg Phe Tyr Gly Leu Met
Advantageously, the above peptide skeleton is in amidated form at its COOH-terminal end, and corresponds in this case to ranakinin as isolated from Rana ridibunda frog brain.
In view of their membership of the tachykinin family, the peptides according to the invention, and especially ranakinin, are capable of involvement in vivo in the transmission of nociceptive information, but can also, like other tachykinins, be involved in blood pressure, inflammation, salivation, contraction of smooth muscle and the regulation of dopaminergic transmission in the nigrostriatal complex.
These functional interactions of tachykinins are carried out through binding to a receptor. The peptides according to the invention are capable of binding to receptors of the NK-1 type described by LAVIELLE et al. (Fondam. Clin. Pharmacol. 1990, 4, 257-268). They hence behave as NK-1 agonists.
According to a particular embodiment, the invention relates to a peptide as obtained of completion of the following steps:
centrifugation of a frog brain tissue extract at 1600 g for 1 hour at 4.degree. C.; PA1 separation of the peptide fraction; PA1 selection of the peptide fraction reacting with an antiserum in which the polyclonal or monoclonal antibodies recognise the COOH-terminal portion of substance P, this antiserum exhibiting, in addition, a reactivity of less than 0.5% with neurokinin A, neurokinin B and unamidated substance P; PA1 purification by HPLC on a column equilibrated with an acetonitrile/water/trifluoroacetic acid (17.5/82.4/0.1, vol/vol/vol) mixture with a flow rate of 1.5 ml/min, the acetonitrile concentration in the elution solvent being raised to 31.5% during 60 min according to a linear gradient; and PA1 recovery of the peptide thus purified.
Different modifications of the peptide structure of the linkages of amino acids described above may be envisaged within the context of the invention. It is possible, in particular, to arrange to modify a peptide corresponding to one of the above formulae by removal of amino acids from its NH.sub.2 -terminal portion provided that the peptide thus formed retains its capacity to be recognized by antibodies directed towards ranakinin, and preferably remains protected against the aminopeptidases present in the cell environment when it is used in vitro or in vivo.
Also within the scope of the invention is a polypeptide containing a number of amino acid residues not exceeding 40, and preferably 30, characterized in that it comprises one of the peptides described above, and in particular in that it contains, in addition, amino acids which are preferably basic at the N-terminal end and/or at the C-terminal end of this peptide, and permitting amidation of the C-terminal structure thus formed of the polypeptide.
As an example, the above polypeptide can correspond to one of the peptides described previously, to which amino acids such as lysine or arginine or alternatively glycine have been added at the NH.sub.2 -terminal end. At the COOH end of the polypeptide, it is possible to insert an amino acid such as glycine capable of bringing about amidation of the polypeptide and lysine or arginine.
Another modification which may be envisaged consists in synthesizing cyclic analogues of the peptides described above by introducing, for example, cysteine residues into the chosen peptide, where appropriate obtained synthetically, so as to stiffen the peptide structure according to a particular spatial conformation. In this case, the linkage of amino acids whose sequence has been described above can, for example, be modified by introduction of cysteine residues introduced at positions 2 and 5 or at positions 3 and 6 in the sequence.
Another modification which may be envisaged, with the object of avoiding oxidation of the COOH-terminal methionine residue, would consist in replacing it by an norleucine residue.
A polypeptide according to the invention can also be characterized in that it is an oligomer or a polymer of one of the above peptides, or an oligomer composed of different peptides among those defined above, linked via peptide bonds.
To carry out the oligomerisation, it is possible to have recourse to any polymerisation technique commonly used in the peptide field, this polymerisation being carried out until an oligomer or polymer containing the requisite number of monomer units (the monomer consisting, in this instance, of the peptide corresponding to the above formula) for acquisition of the desired antigenicity or immunogenicity is obtained.
One method of oligomerisation or polymerisation of the monomer consists in reaction of the latter with a crosslinking agent such as glutaraldehyde.
It is also possible to have recourse to other methods of oligomerisation or coupling, for example to those involving successive couplings of monomer units, through their carboxyl and amine terminal functions, in the presence of homo- or heterobifunctional coupling agents.
It is also possible, for the production of molecules containing one or more peptide units as defined above, to have recourse to genetic engineering techniques employing microorganisms transformed by a particular nucleic acid comprising corresponding suitable nucleotide sequences.
Depending on the applications for which the peptides according to the invention are intended, it is also possible to envisage intercalating between several amino acids, or even between all the amino acids, of the peptides defined above, dextrorotatory amino acids, and in particular dextrorotatory phenylalanine or dextrorotatory tryptophan, capable of preventing the action of the degradative enzymes in the cell environment and thus of increasing their activity. Another modification in this sense consists in replacing certain amino acids, for example of the proline type, by D-tryptophan.
It is, moreover, understood that the amide group of ranakinin may be substituted, for example, monosubstituted with alkyl, aralkyl or aryl groups, or completely substituted by an ester or nitrile radical.
The modifications made to the peptides of the invention may be carried out in such a way that the peptides or polypeptides thus produced are recognized by polyclonal or monoclonal antibodies recognizing ranakinin.
Since ranakinin has so-called substance P-like activity, inasmuch as it is recognized by antibodies directed towards the COOH-terminal portion of substance P, it is also possible to define a group of peptides and polypeptides or oligomers of the latter, modified relative to ranakinin and defined by their capacity for being recognized by antibodies directed towards the COOH terminal portion of substance P.
Within the context thus specified, the different substitutions or modifications of the peptides and polypeptides of the invention must be envisaged according to the applications for which it is desired to use these compounds. In effect, when a peptide having the peptide skeleton of ranakinin is elongaate at its N-terminal end or at its COOH-terminal end, this peptide can become less accessible to an in vivo receptor. Similarly, its viscosity can increase and can consequently cause a decrease in its bioavailability.
On the other hand, if it is sought to obtain an antagonist of the peptide of the invention or to decrease its activity of binding to a receptor while increasing its antigenicity, it will be highly advisable to carry out substitutions on the parent peptide or to graft amino acid residues at the NH.sub.2 -and/or COOH-terminal ends.
A particular problem linked to the use of neuropeptides, in particular as therapeutic agents, stems from their inability to cross the blood-brain barrier.
The peptides of the invention may hence be used as a research tool in pharmacological models in order to determine what conformations might be likely to mimic the structure of the peptides of the invention and be capable of crossing the blood-brain barrier. In this connection, the invention relates to a molecule, peptide or otherwise, synthetic or natural, having a conformation in aqueous solution resembling that of ranakinin in its natural form, or resembling that of its derivatives corresponding to the definitions of the invention, this molecule having a rigid, non-hydrolysable structure capable of crossing the blood-brain barrier.
The peptides defined above, labelled radioactively, for example by substitution of carbon and/or hydrogen atoms by radioactive atoms, or alternatively by addition of an arm such as the Bolton-Hunter reagent grafted onto a free amine function (BOLTON and HUNTER, Biochem. J. 133, 529-538, 1973) also fall within the scope of the invention.
The invention also relates to polyclonal or monoclonal antibodies, characterized in that they specifically recognise a peptide or a polypeptide according to any one of the above definitions. An antibody possesses the capacity to recognise specifically one of the peptides or polypeptides of the invention provided it enables an antigen-antibody type reaction to be carried out and a complex to be formed with these peptides and polypeptides. A subgroup of antibodies satisfying the above conditions is further defined in that these antibodies do not recognise either the NH.sub.2 -terminal portion of substance P or the NH.sub.2 -terminal portion of neurokinin B.
The invention also relates to the antigen antibody complex in which the antigen corresponds to a peptide according to the invention, the antibody being specific for this peptide or for the group of peptides according to the invention.
The monoclonal antibodies may be obtained by conventional techniques for preparing monoclonal antibodies. The technique of fusion of myeloma cells with spleen cells of an animal (for example a mouse) immunized beforehand with ranakinin or a derivative of this peptide as defined above will generally be employed. The hybridomas resulting from the fusion of the above cells are cultured, and the antibodies which they produce are tested to select those which recognise ranakinin and, where appropriate, in this group, those which are specific for the latter under the conditions corresponding to the above definition.
According to a variant, these monoclonal antibodies can also be produced in ascites in animals.
Different applications of the peptides described above may be envisaged, stemming from the fact that they can be used as an analogue of certain neuropeptide molecules and, in particular, in the case of ranakinin, as a substance P analogue.
The invention relates, in addition, to a nucleic acid, characterized in that it codes for a peptide or polypeptide corresponding to the definitions given on the previous pages, and especially a nucleic acid corresponding to the following sequence: EQU AAR CCN AAY CCN GAR MGN UUY UAY GGN YUN AUG (Seq. ID NO. 1).
There also falls within the scope of the invention a cloning and/or expression vector, characterized in that it is modified with a nucleic acid defined above at a site which is non-essential for its replication, this nucleic acid being placed under the control of regulatory elements, and in particular of a promoter recognized by the polymerases of a cell host in which it is desired to clone or express it. The invention also relates to a cell host, characterized in that it is transformed by a vector described above.
As an example of cell hosts which are especially advantageous for carrying out the invention, there are E. coli and eukaryotic cells.
It is possible, in particular, to use the cloning vector ZAP, which by itself combines many of the advantages possessed by other insertion vectors, the vector being modified with the sequence of the invention: apart from the property of being converted in vivo into plasmid Bluescript SK, it permits rapid sequencing of the nucleic acid, riboprobe production, directed mutagenesis and the expression of fusion proteins. E. coli strain BB4 is especially recommended for the propagation of ZAP. Other cloning vectors and host cells which are of interest in the context of the invention are listed in the work Molecular Cloning by Maniatis et al. (1989).
The invention also relates advantageously to the eukaryotic cells transfected by the nucleotide sequence defined above under the control of a eukaryotic gene promoter (for example the promoter of the metallothionein gene, inducible with cadmium).
The peptides according to the invention may be purified from extracts of the brain of frogs such as Rana ridibunda, or alternatively be prepared by conventional techniques in the field of peptide synthesis. This synthesis may be carried out in homogeneous solution or on a solid phase.
For example, the technique of synthesis in homogeneous solution described by HOUBEN-WEYL in the work entitled "Methoden der Organischen Chemie" [Methods in Organic Chemistry] edited by E. Wunsch, Vol. 15-I and II, THIEME, Stuttgart 1974, may be employed.
This method of synthesis consists in condensing the successive aminoacyl residues successively in pairs in the requisite order, or in condensing aminoacyl residues and fragments so prepared beforehand, on the understanding that care will have been taken to protect beforehand all the reactive groups carried by these aminoacyl residues or fragments, with the exception of the amine functions of one and the carboxyl functions of the other, or vice versa, which are normally to participate in the formation of the peptide bonds, in particular after activation of the carboxyl function, according to methods well known in peptide synthesis. As a variant, coupling reactions employing conventional coupling reagents of the carbodiimide type, for example, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide, may be employed. When the aminoacyl residue employed possesses an additional acidic function (in particular in the case of glutamic acid, these functions will, for example, be protected with t-butyl ester groups.
In the case of progressive synthesis, amino acid by amino acid, the synthesis preferably begins with the condensation of the C-terminal amino acid with the amino acid corresponding to the neighboring aminoacyl residue in the desired sequence, and so on, stepwise, up to the N-terminal amino acid. According to another preferred technique of the invention, that described by R. D. MERRIFIELD in the paper entitled "Solid phase peptide synthesis" (J. Am. Soc., 45, 2149-2154) is employed.
To manufacture a peptide chain according to MERRIFIELD's method, a highly porous polymeric resin is employed, to which the first C-terminal amino acid of the chain is bound. This amino acid is bound to the resin via its carboxyl group, and its amine function is protected, for example with a t-butyloxycarbonyl group.
When the first C-terminal amino acid is bound in this manner to the resin, the group protecting the amine function is removed by washing the resin with an acid.
In the case where the group protecting the amine function is a t-butyloxycarbonyl group, it may be removed by treating the resin using trifluoroacetic acid.
The second amino acid which provides the second aminoacyl residue of the desired sequence, starting from the C-terminal aminoacyl residue, is then coupled onto the deprotected amine function of the first C-terminal amino acid bound to the chain. Preferably, the carboxyl function of this second amino acid is activated, for example with dicyclohexylcarbodiimide, and the amine function is protected, for example with t-butyloxycarbonyl.
The first portion of the desired peptide chain, which contains two amino acids and in which the terminal amine function is protected, is thereby obtained. As before, the amine function is deprotected and it is then possible to carry out the binding of the third aminoacyl residue, under conditions similar to those for the addition of the second C-terminal amino acid.
The amino acids which will make up the peptide chain are thus bound, one after another, to the amine group, each time deprotected beforehand, of the portion the peptide chain already formed, and which is attached to the resin.
When the whole of the desired peptide chain has been formed, the groups protecting the different amino acids making up the peptide chain are removed and the peptide is detached from the resin, for example using hydrofluoric acid.